The utilization of CO2 as a feedstock for the production of commodity chemicals potentially offers a more cost effective and renewable alternative to fossil fuel based carbon sources in the chemical industry. Unfortunately, the kinetic and thermodynamic stability of CO2 has limited its exploitation thus far to a handful of commercial chemicals. One method to surmount this stability is the reduction of CO2 via coupling to other relatively high energy small molecules. The functionalization of CO2 with light olefins to produce α,β-unsaturated carboxylic acids is yet another intriguing target for this methodology, with potentially significant implications for the manufacture of acrylates used in superabsorbent polymers, elastomers, and detergents.
Transition metal promoted coupling of CO2 and ethylene toward acrylate formation has been explored as an alternative to currently used propylene oxidation technology since the seminal reports of Hoberg and Carmona in the 1980's (Illustration 1). These pioneering investigators independently pursued new routes for CO2-ethylene coupling using zerovalent nickel and group VI metals, respectively, though catalytic activity remained elusive.

Limbach and co-workers have reported circumventing barriers to β-hydride elimination by adding external bases such as sodium tert-butoxide to diphosphine nickelalactone species which are believed to deprotonate the β-hydrogen directly without necessitating transfer of the hydride to nickel. This approach affords sodium acrylate (NaCO2CHCH2) in good yield and by repeated sequential additions of CO2, ethylene and base several equivalents of sodium acrylate may be obtained in one reaction vessel. Unfortunately, the strong sodium base required for the deprotonation is not compatible with the high CO2 pressure needed for nickelalactone formation, obviating catalytic production under a constant set of reaction conditions.